

<!DOCTYPE html>
<!--[if IE]><![endif]-->
<html>
<head>
  <meta charset="utf-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1">
  <title>New in React v0.4: Prop Validation and Default Values - React Blog</title>
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <meta property="og:title" content="New in React v0.4: Prop Validation and Default Values - React Blog">
  <meta property="og:type" content="article">
  <meta property="og:url" content="https://facebook.github.io/react/blog/2013/07/11/react-v0-4-prop-validation-and-default-values.html">
  <meta property="og:image" content="https://facebook.github.io/react/img/logo_og.png">
  <meta property="og:description" content="Many of the questions we got following the public launch of React revolved around props, specifically that people wanted to do validation and to make sure their components had sensible defaults.
">
  <meta property="fb:app_id" content="623268441017527">

  <link rel="shortcut icon" href="/react/favicon.ico">
  <link rel="alternate" type="application/rss+xml" title="React" href="https://facebook.github.io/react/feed.xml">

  <link rel="stylesheet" href="//cdn.bootcss.com/docsearch.js/1.3.0/docsearch.min.css" />
  <link rel="stylesheet" href="/react/css/syntax.css">
  <link rel="stylesheet" href="/react/css/codemirror.css">
  <link rel="stylesheet" href="/react/css/react.css">

  <script src="//use.typekit.net/vqa1hcx.js"></script>
  <script>try{Typekit.load();}catch(e){}</script>

  <!--[if lte IE 8]>
  <script src="https://unpkg.com/html5shiv@3.7.3/dist/html5shiv.min.js"></script>
  <script src="https://unpkg.com/es5-shim@4.5.9/es5-shim.min.js"></script>
  <script src="https://unpkg.com/es5-shim@4.5.9/es5-sham.min.js"></script>
  <![endif]-->

  <script src="//cdn.bootcss.com/docsearch.js/1.5.0/docsearch.min.js"></script>
  <script src="//cdn.bootcss.com/codemirror/5.15.2/codemirror.js"></script>
  <script src="//cdn.bootcss.com/codemirror/5.15.2/mode/javascript/javascript.js"></script>
  <script src="//cdn.bootcss.com/codemirror/5.15.2/mode/xml/xml.js"></script>
  <script src="//cdn.bootcss.com/codemirror/5.15.2/mode/jsx/jsx.js"></script>
  <script src="//cdn.bootcss.com/react/15.5.4/react.min.js"></script>
  <script src="//cdn.bootcss.com/react/15.5.4/react-dom.min.js"></script>
  <script src="//cdn.bootcss.com/babel-standalone/6.15.0/babel.min.js"></script>

  <script src="/react/js/live_editor.js"></script>
</head>
<body>

  <div class="container">

    <div class="nav-main">
  <div class="wrap">
    <a class="nav-home" href="/react/">
      <img class="nav-logo" src="/react/img/logo.svg" width="36" height="36">
      React
    </a>
    <div class="nav-lists">
      <ul class="nav-site nav-site-internal">
        <li><a href="/react/docs/hello-world.html">Docs</a></li>
        <li><a href="/react/tutorial/tutorial.html">Tutorial</a></li>
        <li><a href="/react/community/support.html">Community</a></li>
        <li><a href="/react/blog/" class="active">Blog</a></li>
        <li class="nav-site-search">
          <input id="algolia-doc-search" type="text" placeholder="Search docs..." />
        </li>
      </ul>
      <ul class="nav-site nav-site-external">
        <li><a href="https://github.com/facebook/react">GitHub</a></li>
        <li><a href="https://github.com/facebook/react/releases">v15.5.4</a></li>
      </ul>
    </div>
  </div>
</div>


    <section class="content wrap blogContent">

  <div class="inner-content">
    

<h1>

  New in React v0.4: Prop Validation and Default Values

</h1>

<p class="meta">
  July 11, 2013
  by
  
    
      <a href="https://twitter.com/zpao">Paul O’Shannessy</a>
    
    
  
</p>

<hr>

<div class="post">
  <p>Many of the questions we got following the public launch of React revolved around <code>props</code>, specifically that people wanted to do validation and to make sure their components had sensible defaults.</p>

<h2>Validation</h2>

<p>Oftentimes you want to validate your <code>props</code> before you use them. Perhaps you want to ensure they are a specific type. Or maybe you want to restrict your prop to specific values. Or maybe you want to make a specific prop required. This was always possible — you could have written validations in your <code>render</code> or <code>componentWillReceiveProps</code> functions, but that gets clunky fast.</p>

<p>React v0.4 will provide a nice easy way for you to use built-in validators, or to even write your own.</p>
<div class="highlight"><pre><code class="language-js" data-lang="js"><span class="nx">React</span><span class="p">.</span><span class="nx">createClass</span><span class="p">({</span>
  <span class="nx">propTypes</span><span class="o">:</span> <span class="p">{</span>
    <span class="c1">// An optional string prop named &quot;description&quot;.</span>
    <span class="nx">description</span><span class="o">:</span> <span class="nx">React</span><span class="p">.</span><span class="nx">PropTypes</span><span class="p">.</span><span class="nx">string</span><span class="p">,</span>

    <span class="c1">// A required enum prop named &quot;category&quot;.</span>
    <span class="nx">category</span><span class="o">:</span> <span class="nx">React</span><span class="p">.</span><span class="nx">PropTypes</span><span class="p">.</span><span class="nx">oneOf</span><span class="p">([</span><span class="s1">&#39;News&#39;</span><span class="p">,</span><span class="s1">&#39;Photos&#39;</span><span class="p">]).</span><span class="nx">isRequired</span><span class="p">,</span>

    <span class="c1">// A prop named &quot;dialog&quot; that requires an instance of Dialog.</span>
    <span class="nx">dialog</span><span class="o">:</span> <span class="nx">React</span><span class="p">.</span><span class="nx">PropTypes</span><span class="p">.</span><span class="nx">instanceOf</span><span class="p">(</span><span class="nx">Dialog</span><span class="p">).</span><span class="nx">isRequired</span>
  <span class="p">},</span>
  <span class="p">...</span>
<span class="p">});</span>
</code></pre></div>
<h2>Default Values</h2>

<p>One common pattern we&#39;ve seen with our React code is to do something like this:</p>
<div class="highlight"><pre><code class="language-js" data-lang="js"><span class="nx">React</span><span class="p">.</span><span class="nx">createClass</span><span class="p">({</span>
  <span class="nx">render</span><span class="o">:</span> <span class="kd">function</span><span class="p">()</span> <span class="p">{</span>
    <span class="kd">var</span> <span class="nx">value</span> <span class="o">=</span> <span class="k">this</span><span class="p">.</span><span class="nx">props</span><span class="p">.</span><span class="nx">value</span> <span class="o">||</span> <span class="s1">&#39;default value&#39;</span><span class="p">;</span>
    <span class="k">return</span> <span class="o">&lt;</span><span class="nx">div</span><span class="o">&gt;</span><span class="p">{</span><span class="nx">value</span><span class="p">}</span><span class="o">&lt;</span><span class="err">/div&gt;;</span>
  <span class="p">}</span>
<span class="p">});</span>
</code></pre></div>
<p>Do this for a few <code>props</code> across a few components and now you have a lot of redundant code. Starting with React v0.4, you can provide default values in a declarative way:</p>
<div class="highlight"><pre><code class="language-js" data-lang="js"><span class="nx">React</span><span class="p">.</span><span class="nx">createClass</span><span class="p">({</span>
  <span class="nx">getDefaultProps</span><span class="o">:</span> <span class="kd">function</span><span class="p">()</span> <span class="p">{</span>
    <span class="k">return</span> <span class="p">{</span>
      <span class="nx">value</span><span class="o">:</span> <span class="s1">&#39;default value&#39;</span>
    <span class="p">};</span>
  <span class="p">}</span>
  <span class="p">...</span>
<span class="p">});</span>
</code></pre></div>
<p>We will use the cached result of this function before each <code>render</code>. We also perform all validations before each <code>render</code> to ensure that you have all of the data you need in the right form before you try to use it.</p>

<hr>

<p>Both of these features are entirely optional. We&#39;ve found them to be increasingly valuable at Facebook as our applications grow and evolve, and we hope others find them useful as well.</p>

</div>


  <div class="fb-like" data-send="true" data-width="650" data-show-faces="false"></div>


  </div>
  <div class="nav-docs nav-blog">
  <div class="nav-docs-section">
    <h3>Recent posts</h3>
    <ul>
      
        <li><a href="/react/blog/2017/04/07/react-v15.5.0.html">React v15.5.0</a></li>
      
        <li><a href="/react/blog/2016/11/16/react-v15.4.0.html">React v15.4.0</a></li>
      
        <li><a href="/react/blog/2016/09/28/our-first-50000-stars.html">Our First 50,000 Stars</a></li>
      
        <li><a href="/react/blog/2016/08/05/relay-state-of-the-state.html">Relay: State of the State</a></li>
      
        <li><a href="/react/blog/2016/07/22/create-apps-with-no-configuration.html">Create Apps with No Configuration</a></li>
      
        <li><a href="/react/blog/2016/07/13/mixins-considered-harmful.html">Mixins Considered Harmful</a></li>
      
        <li><a href="/react/blog/2016/07/11/introducing-reacts-error-code-system.html">Introducing React's Error Code System</a></li>
      
        <li><a href="/react/blog/2016/04/08/react-v15.0.1.html">React v15.0.1</a></li>
      
        <li><a href="/react/blog/2016/04/07/react-v15.html">React v15.0</a></li>
      
        <li><a href="/react/blog/2016/03/29/react-v0.14.8.html">React v0.14.8</a></li>
      
      <li><a href="/react/blog/all.html">All posts ...</a></li>
    </ul>
  </div>
</div>

</section>


    <footer class="nav-footer">
  <section class="sitemap">
    <a href="/react/" class="nav-home">
    </a>
    <div>
      <h5><a href="/react/docs/">Docs</a></h5>
      <a href="/react/docs/hello-world.html">Quick Start</a>
      <a href="/react/docs/thinking-in-react.html">Thinking in React</a>
      <a href="/react/tutorial/tutorial.html">Tutorial</a>
      <a href="/react/docs/jsx-in-depth.html">Advanced Guides</a>
    </div>
    <div>
      <h5><a href="/react/community/support.html">Community</a></h5>
      <a href="http://stackoverflow.com/questions/tagged/reactjs" target="_blank">Stack Overflow</a>
      <a href="https://discuss.reactjs.org/" target="_blank">Discussion Forum</a>
      <a href="https://discord.gg/0ZcbPKXt5bZjGY5n" target="_blank">Reactiflux Chat</a>
      <a href="https://www.facebook.com/react" target="_blank">Facebook</a>
      <a href="https://twitter.com/reactjs" target="_blank">Twitter</a>
    </div>
    <div>
      <h5><a href="/react/community/support.html">Resources</a></h5>
      <a href="/react/community/conferences.html">Conferences</a>
      <a href="/react/community/videos.html">Videos</a>
      <a href="https://github.com/facebook/react/wiki/Examples" target="_blank">Examples</a>
      <a href="https://github.com/facebook/react/wiki/Complementary-Tools" target="_blank">Complementary Tools</a>
    </div>
    <div>
      <h5>More</h5>
      <a href="/react/blog/">Blog</a>
      <a href="https://github.com/facebook/react" target="_blank">GitHub</a>
      <a href="http://facebook.github.io/react-native/" target="_blank">React Native</a>
      <a href="/react/acknowledgements.html">Acknowledgements</a>
    </div>
  </section>
  <a href="https://code.facebook.com/projects/" target="_blank" class="fbOpenSource">
    <img src="/react/img/oss_logo.png" alt="Facebook Open Source" width="170" height="45"/>
  </a>
  <section class="copyright">
    Copyright © 2017 Facebook Inc.
  </section>
</footer>

  </div>

  <div id="fb-root"></div>
  <script src="/react/js/anchor-links.js"></script>
  <script>
    

    

    
    docsearch({
      apiKey: '36221914cce388c46d0420343e0bb32e',
      indexName: 'react',
      inputSelector: '#algolia-doc-search'
    });
  </script>
</body>
</html>
